#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;

int main()
{
  int n;
  cin >> n;
  int a = 2,b = 1;
  double ret = 0;
  while(n--)
  {
  	ret += a*1.0/b;
  	int tmp = a;
  	a = a+b;
  	b = tmp;
  	
  }
  printf("%.4f",ret);
}

